不喜欢括号

python解法，使用递归来做的：

从左到右读，如果遇到加减乘除符号，向后看两个，如果这两个数都是整数，那么直接开始计算。计算完后，进行下一个递归。

def calc(arr):
    for i,v in enumerate(arr):
        if v in ["+","-","*","/"]:
            if arr[i+1].isnumeric() and arr[i+2].isnumeric():
                return calc(arr[:i]+[str(int(eval(arr[i+1]+v+arr[i+2])))]+arr[i+3:])
    return arr[0]


while True:
    try:
        a,b=input(),input().split()
        print(calc(b))
    except:
        break

import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		while (sc.hasNext()) {
			int n = sc.nextInt();
			String[] arr = new String[n];
			Stack<Integer> stack = new Stack<>();
			for (int i = 0; i < n; i ++ )
				arr[i] = sc.next();
			for (int i = n - 1; i >= 0; i -- ) {
				if(arr[i].equals("+")) stack.push(stack.pop() + stack.pop());
				else if(arr[i].equals("-")) stack.push(stack.pop() - stack.pop());
				else if(arr[i].equals("*")) stack.push(stack.pop() * stack.pop());
				else if(arr[i].equals("/")) stack.push(stack.pop() / stack.pop());
				else stack.push(Integer.parseInt(arr[i]));
			}
			System.out.println(stack.pop());
		}
	}
}

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<functional>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <exception>
#include <iomanip>
#include <memory>
#include <sstream>
#include <list>

using namespace std;

int main(int argc, char** argv)
{
	//freopen("in.txt", "r", stdin);
	int n;
	while (cin >> n)
	{
		vector<string> pre;
		string s;
		for (int i = 0; i < n; ++i)
		{
			cin >> s;
			pre.emplace_back(s);
		}
		while (pre.size() > 1)
		{
			for (int i = pre.size() - 1; i >= 0;--i)
			{
				string op = pre[i];
				if (op == "+" || op == "-" || op == "*" || op == "/")
				{
					int x = stoi(pre[i + 1]), y = stoi(pre[i + 2]);
					switch (op[0])
					{
					case '+': x += y; break;
					case '-': x -= y; break;
					case '*': x *= y; break;
					case '/': x /= y; break;
					default:break;
					}
					pre[i] = to_string(x);
					pre.erase(pre.begin() + i + 1, pre.begin() + i + 3);
					break;
				}
			}
		}

		cout << pre[0] << endl;
	}

	return 0;
}

//利用堆栈；从右向左扫面输入的字符串：如果是数字的话，数字进栈；
//符号的话，弹出栈顶的两个元素做运算，运算结果进栈
#include<iostream>
#include<stack>
#include<string>
#include<vector>
using namespace std;
int main() {
	int n,i,a,b,t;
	
	stack<int> ret;

	while(cin>>n) {
		if(n==0)
			continue;
		vector<string> v(n);
		i=0;
		while(i<n) {
			cin>>v[i++];
		}
		for(i=n-1; i>=0; i--) {
			if(v[i].compare("+")==0) {
				a=ret.top();
				ret.pop();
				b=ret.top();
				ret.pop();
				ret.push(a+b);
			} else if(v[i].compare("-")==0) {
				a=ret.top();
				ret.pop();
				b=ret.top();
				ret.pop();
				ret.push(a-b);
			} else if(v[i].compare("*")==0) {
				a=ret.top();
				ret.pop();
				b=ret.top();
				ret.pop();
				ret.push(a*b);
			} else if(v[i].compare("/")==0) {
				a=ret.top();
				ret.pop();
				b=ret.top();
				ret.pop();
				ret.push(a/b);
			} else {
			//	cout<<v[i]<<endl;
				ret.push(atoi(v[i].c_str()));
			}
		}
		cout<<ret.top()<<endl;
		v.clear();
		while(!ret.empty()){
			ret.pop();
		}
	}
	return 0;
}

// write your code here cpp
#include<cstdio>
(802)#include<stack>
#include<cstring>
(803)#include<cctype>
using namespace std;
int main(){
    char str[60][20];
    int n;
    while(scanf("%d",&n)!=EOF){
        stack<int> s;
        for(int i=0;i<n;++i){
            scanf("%s",str[i]);
        }
        for(int i=n-1;i>=0;--i){
            if(isdigit(str[i][0])){
                int sum=0;
                for(int j=0;j<strlen(str[i]);++j){
                    sum=sum*10+str[i][j]-'0';
                }
                s.push(sum);
            }else{
                int a=s.top();
                s.pop();
                int b=s.top();
                s.pop();
                int sum;
                if(str[i][0]=='+')
                    sum=a+b;
                else if(str[i][0]=='-')
                    sum=a-b;
                else if(str[i][0]=='*')
                    sum=a*b;
                else
                    sum=a/b;
                s.push(sum);
            }
        }
        printf("%d\n",s.top());
    }
}

import java.util.Scanner;
import java.util.Stack;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int n = sc.nextInt();
            Stack<Node> nodeStack = new Stack<>();
            Node root = null;
            for (int i = 0; i < n; i++) {
                if (i == 0) {
                    Node newNode = new Node(sc.next());
                    nodeStack.push(newNode);
                    root = newNode;
                } else {
                    Node pNode = nodeStack.peek();
                    Node newNode = new Node(sc.next());
                    if (pNode.lchild == null) {
                        pNode.lchild = newNode;
                    } else if (pNode.rchild == null) {
                        pNode.rchild = newNode;
                        nodeStack.pop();
                    }
                    if (!newNode.isLeaf) {
                        nodeStack.push(newNode);
                    }
                }
            }
            System.out.println(root.getValue());
        }
        sc.close();
    }

    static class Node {
        Node lchild, rchild;
        String val;
        int intVal;
        boolean isLeaf = true;
        public Node(String val) {
            this.val = val;
            try {
                this.intVal = Integer.parseInt(this.val);
            } catch (Exception e) {
                isLeaf = false;
            }
        } 
        int getValue() {
            if (isLeaf) {
                return intVal;
            }
            switch (val) {
                case "+":
                    return lchild.getValue() + rchild.getValue();
                case "-":
                    return lchild.getValue() - rchild.getValue();
                case "*":
                    return lchild.getValue() * rchild.getValue();
                default:
                    return lchild.getValue() / rchild.getValue();
            }
        }
    }
}

	

#include <bits/stdc++.h>
using namespace std;

long long atoi(string s) {
    long long res = 0;
    for (int i = 0; i < s.size(); ++i) {
        res = res * 10 + s[i] - '0';
    }
    return res;
}

int main() {
    int n;
    while (cin >> n) {
        string s[50];
        stack<long long> num;
        for (int i = 0; i < n; ++i) {
            cin >> s[i]; 
        }
        for (int i = n - 1; i >= 0; --i)
            if (s[i] == "+" || s[i] == "-" || s[i] == "*" || s[i] == "/") {
                long long left = num.top();
                num.pop();
                long long right = num.top();
                num.pop();
                if (s[i] == "+")
                    left += right;
                else if (s[i] == "-") 
                    left -= right;
                else if (s[i] == "*") 
                    left *= right;
                else 
                    left /= right;
                num.push(left);
            }
            else {
                num.push(atoi(s[i]));
            }
        cout << num.top() << endl;
    }
    return 0;
}

import java.util.Scanner;
import java.util.Stack;

public class Main {
	private static Scanner scan = new Scanner(System.in);
	public static void main(String[] args) {
		while(scan.hasNext()){
			Stack<String> stackStr = new Stack<>();//暂存所有字符
			Stack<Integer> stack = new Stack<>();//暂存运算数字
			
			int n = Integer.parseInt(scan.next());
			for(int i = 1; i <= n; ++i)
				stackStr.push(scan.next());
			
			for(int i = 1; i <= n; ++i){
				String str = stackStr.pop();
				//判断是否是数字
				if (Character.isDigit(str.charAt(0))) {
					stack.push(Integer.parseInt(str));
				} else {
					char c = str.charAt(0);
					int a = stack.pop();
					int b = stack.pop();
					switch (c) {
					case '+':
						stack.push(a+b);
						break;
					case '-':
						stack.push(a-b);
						break;
					case '*':
						stack.push(a*b);
						break;
					case '/':
						stack.push(a/b);
						break;
					}
				}
			}
			System.out.println(stack.pop());
		}
	}
}

这个代码输入哪个“前缀表达式”会发生溢出？


#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <functional>
#include <algorithm>
#include <numeric>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <sstream>
using namespace std;
void myPush (stack<char> &st, char bas);
char cal (int one, int two, char opchar);
char cal (int one, int two, char opchar)
{
	switch (opchar)
	{
		case '+':
			return one + two + 48;
		case '-':
			return one - two + 48;
		case '*':
			return one * two + 48;
		case '/':
		{
			if (0 == two)
			{
				return 0;
			}
			return one / two + 48;
		}
		default:
		{
			cout << "输入有误" << endl;
			return 0;
		}
	}
}
void myPush (stack<char> &st, char bas)
{
		if (st.empty () || st.top () < '0' || st.top () > '9' || bas < '0' || bas > '9')
		{
			st.push (bas);
		}
		else
		{
			int one = st.top () - 48;
			int two = bas - 48;
			st.pop ();
			char opchar = st.top ();
			st.pop ();
			char ret = cal (one, two, opchar);
			myPush (st, ret);
		}
}
int main ()
{
	int n;
	while (scanf ("%d", &n) != EOF)
	{
		char bas;
		stack<char> st;
		for (int x = 0; x < n; x++)
		{
			cin >> bas;
			myPush (st, bas);
		}
		cout << st.top() - 48 << endl;
	}
	return 0;
} 

import java.util.Scanner;
import java.util.Stack;
public class Main {
	public static void main(String[] args) {
		try(Scanner scanner = new Scanner(System.in)){
			while(scanner.hasNext()){
				int n = Integer.parseInt(scanner.next());
				Stack<String> inStack = new Stack<>();
				Stack<Integer> stack = new Stack<>();
				for(int i=0;i<n;i++){
					String input = scanner.next();
					inStack.push(input);
				}
				while(inStack.size()>0){
					String input = inStack.pop();
					char c = input.charAt(0);
					if(c>='0'&&c<='9'){
						stack.push(Integer.parseInt(input));
					}else{
						int a = stack.pop();
						int b = stack.pop();
						switch(c){
						case '+':stack.push(a+b);break;
						case '-':stack.push(a-b);break;
						case '*':stack.push(a*b);break;
						case '/':stack.push(a/b);break;
						}
					}
				}
				System.out.println(stack.pop());
			}
		}
	}
}